A standard power feature of a motor vehicle is a power opener/closer for the trunk lid, hatch back, or similar panel. The panel in question is normally mounted generally pivotally, typically by means of curved arms, for movement between a closed position sitting flush in its opening and an open position giving access to the opening. The mechanism can normally be actuated for opening by means of the vehicle's remote controller that also unlocks the passenger and driver doors. It is normally set to close when pushed down into a partially closed position. Thus the user can pop the trunk remotely, making it easy to load without having to put down whatever is going into the trunk to have hands free for operating the trunk latch, and easy to close in that the user need merely push it down somewhat, whereupon the power operator will take over and pull the panel to and latch it.
In a typical such system as described in U.S. Pat. No. 4,851,742 of Chapman the panel, here a trunk lid, is urged into the open position by a spring strong enough to raise the lid all the way up. A motor has a drive wheel or pulley around which is secured a cable whose outer end is attached to the door offset from the hinge so that when the cable is payed out the spring opens the panel and when the cable is wound up the door is pulled down against the force of the spring.
The problem with such a system is that it is fairly common for something, for instance the objects loaded into the trunk, to block full closing of the door. In this case the door will stop in a partially closed position. To prevent the motor from burning out, as the motor is normally shut off by automatic actuation of a switch as the panel reaches its fully closed position, a current-monitoring system is connected to the operator's controller. Thus, when the controller senses excess current consumption indicating that the motor is operating against too great a load, the motor is shut off and a warning signal is emitted.
This system is relatively complex. The motor has to be very powerful since it serves to operate against the spring on closing, although it only acts as a brake on opening. The opening movement is wholly the responsibility of the spring which must be very powerful. Finally the system is subject to damage if the panel is moved forcibly during an opening or closing cycle, if for instance a person tries to stop or raise the lid as it is closing.
Another system described in U.S. Pat. No. 2,850,140 of Compeau has a releasable coupling device which decouples the operator from the drive when closing of the door is impeded or some force operates opposite the closing force. While this system effectively protects the operator motor without the complexity of a current-monitoring system, once it decouples it leaves the power-closing feature inoperative. Recoupling the operator is a relatively complex job normally only undertaken by trained service personnel.